1. Field of the Invention
The present invention relates to a process for separating at least one component from a gaseous mixture by adsorption and to an apparatus for carrying out the process. The separation process is of the type wherein a gaseous mixture is circulated through an adsorbent mass with cyclical pressure variations, and the highest pressure level of the cycle is at least twice the lowest pressure level. The adsorbent mass is one of a plurality of adsorbent masses.
2. Description of the Prior Art
In a known adsorption process, the different adsorbent masses are placed in a plurality of drums with or without an auxiliary storage accumulator according to the pressure cycle.
The advantage of such a process is that it provides a good yield with low energy consumption. However, the productivity (measured in Nm.sup.3 /h of gas produced per m.sup.3 of adsorbent) remains low. The production of oxygen from the separation of air has a productivity which is presently in the area of 15 Nm.sup.3 /h/m.sup.3.
In order to provide a higher performance cycle (in terms of yield and energy required for the separation), it is necessary to provide the largest possible number of drums (adsorbers) in order to operate a complex cycle, thus considerably increasing the investment cost. A compromise setup includes two or three adsorbers to produce oxygen from the separation of air.
An industrial application requires, therefore, at least two adsorbers and generally three in order to fully employ the rotating machinery, such as compressors, vacuum pumps along with the necessary piping valves, some of which must be regulator valves, and a computer to operate the cycle. However, the cost of such a unit is high, especially in the light of the cost of the adsorbent material which must thus be provided in large quantities.
In order to reduce the cost, one solution comprises the reduction of the cycle time in order that the adsorbent can be used more efficiently and thus proportionally reduce the quantity necessary per cycle. However, this poses further problems, one of which is the valves which must be operated more often, thereby increasing the wear because they have to be opened and closed in very brief periods, thus increasing their cost. Furthermore, the frequency of attrition through wear of the adsorption material requires that the contact surfaces be increased and that the height of the adsorbent material bed be reduced which leads to complex and expensive adsorbers. As far as attempting to maintain high performance is concerned, it is noted that the adsorption kinetics is penalized when a short duration is required, and in order to overcome this problem, the granulometry of the particles of the adsorbent material must be reduced, which thus aggravates the previously mentioned problems.
Actually, to our knowledge, there is no industrial installation of this type having an oxygen production above 5 tons per day which utilizes a cycle of less than 2.times.45 seconds with two adsorbers.
In order to overcome these inconveniences, a certain number of solutions have been proposed but have not led to date to industrial applications.
One such solution which has been proposed utilizes a process of very rapid pressure variations or processes referred to as "Parametric Pumping". Such processes use a very short cycle (less than 1 second to a few seconds) on adsorbent beds of adsorbent particles of fine granulometry. The separation of oxygen from air in particular can be obtained by pressure waves. This process allows very high productivity in the 100 Nm.sup.3 /h/m.sup.3 range, but it is very costly energy-wise and has a low yield. Moreover, the attrition phenomenon of the adsorbent is worrisome, and switching valves are required which can perform sometimes every 1/10th of a second.
Rotating valves or distributors exist which feed adsorbers disposed in a circle or cylindrical adsorbers arranged in angular sectors in order to reduce the number of valves and piping and bring the process to more or less a continuous process. However, the gas circulation in these devices is generally longitudinal of the adsorber. Thus, the cycle duration is lengthy, and the resulting cycles are rudimentary, utilizing a rotating distributor technology and thus of low performance. The productivity of such devices is comparable to conventional processes.
A rotary adsorber is also known which functions intermittently and is divided up in angular sectors, with longitudinal circulation of the gas. The quantity and quality of the adsorbent sieves located in the center thereof for an industrial setup are incompatible with rotary technology. An ozone production system has been described in International Patent Application PCT WO 86/06056 using an adsorption separation to separate ozone from a mixture of oxygen and ozone, in which there is a diagram showing the adsorbent material arranged in sectorial compartments rotating around a vertical axis with horizontal circulation of the gas. However, such a system requires considerable fine tuning if it is desired to implement such a process with its high pressure variations between the highest pressure level and the lowest pressure level of the cycle as well as the provision of much more elaborate cycles.